Research has found that treatment programmes for veterans with Post-Traumatic Stress Disorder (PTSD) have high rates of drop-out and are often not as effective as in other populations. Previous findings suggested that group cohesion during treatment significantly predicted outcomes for the military personnel receiving treatment. This research intends to assess what facilitates a veteran with PTSD to successfully complete a residential treatment programme. This study aims to qualitatively investigate the impact, and experiences of being part of a cohort within an intensive treatment of UK veterans diagnosed with PTSD. The study recruited eight participants who successfully completed this form of treatment from a veteran’s mental health charity. Semi-structured telephone interviews were conducted. Thematic analysis (TA) was used to analyse the qualitative data. Four key themes emerged: (a) <em>Cohort relationships</em>; knowing each other well, motivate and support each other, communication, sharing information and advice, and the effects of a non-cohesive cohort. (b) <em>Cohort dynamics</em>; negative moods and attitudes, the combination of people in a cohort, motivation for change, and division between cohorts, (c) <em>Shared experience</em>; “in the same boat”, the unique bond shared between veterans, and having similar military experiences, and (d) <em>Containment</em>; living in a bubble, support after 1:1 therapy, learning skills, the whole package of treatment and treatment intensity. The impact of being part of a veteran cohort whilst undergoing treatment and the ability to relate to each other through shared experiences was deemed as a positive supportive aspect of this treatment, with veterans who significantly benefitted from treatment. Dynamics that can affect this were expressed, such as the impact of negative attitudes. The containing influence of inpatient treatment was discussed as beneficial to opening up within therapy.